Control for mobile construction machine

ABSTRACT

A control for a mobile excavating backhoe comprising a handball including a trigger lever mounted for pivotal movement, a plunger operatively associated therewith, internal passages for permitting pressurized air to flow between inlet, exhaust and signal ports, and a metering or modulating valve regulating the air flow between the inlet, exhaust and signal ports. Pivotal movement of the lever is translated into axial movement of the plunger and the metering valve to produce a variable pressure signal at one of the signal ports in the handball. The signal controls an air cylinder in the pneumatic control system, and the cylinder is connected to a hydraulic control valve which provides the necessary oil pressure for operating a double acting hydraulic cylinder secured to the frame of an earth-moving machine. The magnitude of the variable pressure signal determines the extent of movement of the hydraulic control valve, thus providing proportional control over the functions of the earthmoving machine.

United States Patent [191 Bernhoft et a].

[451 Nov. 20, 1973 [22] Filed:

[ CONTROL FOR MOBILE CONSTRUCTION MACHINE [52] US. Cl 137/627.5, 91/414, 91/434,

180/77 R [51] Int. Cl. 15161: 11/16 [58] Field of Search 60/52 HE; 180/77 R,

180/77 HT; 214/138 R; 137/6275, 637; 91/414, 434, 457, 461, 47; 251/80 [56] References Cited UNITED STATES PATENTS 3,446,376 5/1969 Molby 180/77 R X 2,478,002 8/1949 Mott 91/457 X 2,923,518 2/1960 Goodrich 251/80 X 3,054,386 9/1962 Bohnhofi' 91/434 X 2,346,820 4/1944 Casler et al 91/434 X 3,019,816 2/1962 Larsen et al. 91/434 X 2,535,785 12/1950 Couri 91/475 X Primary Examiner-Robert G. Nilson Att0meyAndrew J. Beck et al.

[5 7] ABSTRACT A control for a mobile excavating backhoe comprising a handball including a trigger lever mounted for pivotal movement, a plunger operatively associated therewith, internal passages for permitting pressurized air to flow between inlet, exhaust and signal ports, and a metering or modulating valve regulating the air flow between the inlet, exhaust and signal ports. Pivotal movement of the lever is translated into axial movement of the plunger and the metering valve to produce a variable pressure signal at one of the signal ports in the handball. The signal controls an air cylinder in the pneumatic control system, and the cylinder is connected to a hydraulic control valve which provides the necessary oil pressure for operating a double acting hydraulic cylinder secured to the frame of an earthmoving machine. The magnitude of the variable pressure signal determines the extent of movement of the hydraulic control valve, thus providing proportional control over thefunctions of the earth-moving machine.

9 Claims, 8 Drawing Figures Patented Nov. 20, 1973 3,773,084

5 Sheets-Sheet 1 INVENTORS GERALD W. BERNHOFT 8.

DAVID A. MILLER Patented Nov. 20, 1973 3 Sheets-Sheet 3 ii; W fii i i1i||% .4 BY 9 W ATTORNEYS CONTROL FOR MOBILE CONSTRUCTION MACHINE BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to improvements in controls for construction and earthmoving machines, and more specifically, to metering controls for mobile excavators such as backhoes and the like.

2. Discussion of Prior Art Known construction and earth-moving machines, such as backhoes, include numerous manually operated control levers manipulated by the machine operator to control the operation of the various machine operations such as bucket curl, dig, hoist and swing functions of a backhoe. The machine operational cycle and the number and location of the control levers for controlling the same are such that the operator has to frequently shift his hands from lever to lever. In order to reduce the number of control levers and simplify, in some measure, the operators task, onoff buttons adapted to pneumatically control curl and dig functions have been positioned on control knobs or handballs on top the control levers for controlling boom hoist and swing functions. Although the use of such handballs reduces the need for an operator to shift hands from lever to lever, it raises several vexing problems. Conventional handballs utilizing on-off control do not permit precise, small adjustment of the bucket position because on-off control thereof is adapted to produce merely a pressure signal of fixed magnitude to the backhoes pneumatic control system. This lack of precise control may be particularly problematical when digging around obstructions and the like.

Additionally conventional handballs with on-off pneumatic controls have been additionally problematical to operators in that such controls become cold in temperature and uncomfortable to touch after repeated use due to expansion of large volumes of pressurized air being vented to atmosphere through the handballs.

SUMMARY Thus, with the operational deficiencies of conventional handballs with on-off buttons clearly in mind, the instant invention contemplates a unique handball to be mounted on construction machinery control levers and including a selectively variable control valve characterized by a trigger lever mounted for pivotal movement atop the handball, a plunger disposed in abutting relationship to the trigger lever, internal passages for permitting pressurized air to flow between inlet, exhaust and signal ports, and a metering or modulating valve for regulating the flow of fluid between the inlet, exhaust and signal ports in response to movement of the trigger lever. The pivotal movement of the trigger lever is translated into axial movement of the plunger which shifts the metering or modulating valve so that an air signal whose magnitude is proportionaito the extent of trigger lever movement is generated. The variable air signal is supplied to a pneumatic control system including inter alia, an actuating air cylinder which adjusts the position of the double acting hydraulic control valve. The hydraulic control valve, in turn, actuates a hydraulic cylinder which controls related functions of an earth-moving machine. The extent of movement of the hydraulic control valve is directly related through the actuating air cylinder to the magnitude of the variable pressure air signal. Furthermore, in addition to the proportional control, the unique handball design affords precise regulation of the speed of performance of the machine functions and substantially reduces the cooling effect experienced with known handballs since less volume of air passes, at a lower pressure, through the new handball device.

Unlike prior art devices, the compactness of the trigger lever and modulating valve of the instant invention permit a pair of trigger levers and a like pair of modulating valves to be operatively associated with a single handball; consequently the machine operator can exercise proportional control over related machine functions with one hand. Furthermore, the handball may be equipped with long air lines and be removable from the operators cab for remote control of dig and bucket functions to allow the operator to stand outside the cab of the machine and peer down into a deep trench.

Other advantages attributable to the instant invention will become apparent to the skilled artisan in light of the following description of the invention when construed in connection with the accompanying sheets of drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical cross-sectional view through a removable handball constructed in accordance with the principles of the instant invention;

7 FIG. 2 is a bottom plan view of the handball, such view being taken along line 2-2 in FIG. 1 and in the direction indicated;

FIG. 3 is a view of a detail of the handball of FIG. 1;

FIG. 4 is a cross-sectional view of the handball, such view being taken along line 4-4 in FIG. I and in the direction indicated;

FIG. 5 is a cross-sectional view of the handball, such view being taken along line 55 in FIG. 1 and in the direction indicated;

FIG. 6 is a front elevational view of the handball of FIG. 1;

FIG. 7 is a schematic representation of the pneumatic and hydraulic circuits controlled by the handball of FIG. I; and

FIG. 8 is a perspective view of the handball of the instant invention shown in combination with control levers of a mobile construction machine.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in greater detail to the drawings wherein identical reference numerals refer to identical elements, FIG. 1 depicts a handball indicated generally by reference character 10 and constructed in accordance with the principles of the instant invention. A threaded opening 12 is formed in the lower surface of the handball, and a control lever 14 is screw threaded into the opening to secure the handball in fixed, yet removable, position atop the lever. A first bore 16 and a second bore 18 extend axially throughout the body of the handball. Since the components located with bores 16 and 18 are identical, only those components located within bore 16 will be described in detail at this juncture.

Trigger lever 20 is retained in position at the upper end of bore 16 by a pin 22. A cylindrical plunger 24 is situated adjacent to the lower end of the trigger lever, and a washer 26 is retained in position near the lower end of the plunger by snap ring 28. A lubricating seal 25 is positioned in a recess in the handball body, and plunger 24 passes therethrough. The washer provides a seat for upper control spring 30 which encircles the reduced-diameter section of plunger 24 and biases the plunger unpwardly.

The lower end of plunger 24 extends into an upwardly opening cavity 32 at the upper end of spacer 34, and washer 26 engages the annular wall of the spacer defining cavity 32. A pin 36 with a threaded upper end is screwed into engagement with a central bore 38 in spacer 34. The lower end of pin 36 terminates in a needle-like segment 37. A sealing washer 40 is snugly held on the upper portion of pin 36 in engagement with the lower face of spacer 34.

A plug 42 is secured to handball at the lower end of bore 16. The innermost end of plug 42 defines an annular seat 44 which cooperates with the lower face of washer 40. An axial passageway 46 extends through the plug and serves as an inlet port, and pin 36 is movable within the passageway. O-rings 48 and 50 are seated in annular recesses in the walls of plug 42 for sealing purposes. An annular passageway 52 communicates with passageway 46 via radial passageway 54, and passageway 54 is in communication with first signal port 55, indicated by dotted lines in FIG. 1. The signal at port 55 is transmitted via conduit 57 to the pneumatic control circuit. Needle-like segment 37 of pin 36 passes through a constricted portion of passageway 46 and contacts ball 56, which is urged by lower control spring 58 upwardly against the shoulder defined by the constriction in passage 46. Threaded nut 59 is screwed into sealing engagement with plug 42 and prevents axial communication therethrough.

Since the components retained with bore 18 are identical to the components retained within bore 16 and both bores are pressurized from a common inlet, the identical components in bore 18 are identified by the prefix 100" plug the same identifying reference numeral. To illustrate, trigger lever 120 is retained at the upper end of bore 18 by a pin 122 and a cylindrical plunger 124 is situated adjacent to the lower end of the trigger lever. Bore 18 further houses dirt seal 125, washer 126, snap ring 128, and upper control spring 130 which encircles the reduced diameter section of plunger 124 and biases the plunger upwardly.

The lower end of plunger 124 extends into cavity 132 at the upper end of spacer 134, and washer 126 engages the annular walls defining the cavity. Pin 136, which terminates in segment 137, is screwed into engagement with central bore 138 in spacer 13 A sealing washer 140 engages the lower face of the spacer.

Plug 142 seals the lower end of bore 18, and the innermost end of the plug defines an annular seat 144. Axial passageway 166 extends through the plug, and O-rings 148 and 150 perform a sealing function. An annular passageway 152 communicates with passageway 146 via radial passageway 154, and passageway 154 is in communication with second signal port 155, which is not visible in FIG. 1 but is clearly indicated in FIGS. 2 and 4. Segment 137 of pin 136 passes through a constricted portion of passageway 146 and contacts ball 156, which is biased upwardly by lower control spring 158.

A conduit 60 is slipped over nipple 62, to supply air to both bores situated within the interior of the handball. Bore 18 is pressurized directly from the axial passage through nipple 62, while bore 16 is pressurized indirectly via radial passageway 70. Passageway 64 communicates with both bores 16 and 18 and opens into exhaust port 66 located adjacent to the upper end of opening 12. Conduit 68 is secured in place at the outer end of port 66. Radial passageway establishes communication between axial passageways 46 and 146 in plugs 42 and 142, respectively, and the exterior of the handball.

H6. 2 shows the underside of handball 10. Opening 12, with control lever 14 seated therein, is visible at the left, and exhaust port 66 is seen in proximity to opening 12. Plug 142 is hexagonal in shape at its outermost surface, and plug 42 is similarly shaped. The single inlet conduit 60 abuts against the hexagonal nut that retains nipple 62 in position and communicates with bores 16 and 18, as previously noted. First signal port 55 communicates with axial passageway 47, while second signal port 155 communicates with axial passageway 146.

FIG. 3 is a view, on an enlarged scale, of a detail of bore 16 showing the metering or modulating valve in its normal, unactuated position. The unactuated position indicates that trigger lever 20 is in its home position of FIG. 1. In its unactuated position, washer 40 is positioned approximately 0.01 inch away from valve seat 44, so that pressurized air that passes ball valve 56 will flow past seat 44, into passage 64, and then exit through exhaust port 66.

The upper end of pin 36 is screw threaded into engagement with bore 38 of spacer 34 (see FIG. 3). The pin can either be advanced upwardly, or lowered, within the bore so as to alter the position of washer 40 relative to annular seat 44. When washer 40 engages seat 44, flow upwardly through axial passageway 46 in plug 42 is blocked and back pressure builds up within the passageway and produces a variable pressure signal at signal port 55. FIG. 4 is taken along a line of sight parallel to the line of sight utilized in FIG. 2. In addition to exhaust port 66, FIG. 4 shows radial passage 54 which connects annular passageway 52 to first signal port 55 and radial passage 154 which connects annular passageway 152 to second signal port 155.

FIG. 5 is taken along a line of sight parallel to the lines of sight utilized in FIGS. 2 and 4. The clearance between washer 26 held in place on the lower end of plunger 24 by snap ring 28 and cavity 32 in spacer 34 is visible. Similarly, the clearance between washer 126 and cavity 132 in spacer 134 is also visible. These clearances are required so that the plunger-s 24 and 124 can be freely moved axially within axial bores 16 and 18 respectively, in response to actuation of trigger levers 20 and 120, respectively.

The manner in which the trigger levers are mounted for pivotal movement is best shown in FIG. 6. Trigger lever 20 can be manually pivoted through the arc indicated by the directional arrows. As shown in dotted outline, knee 260 on lever 20 is resting by its own weight on the upper end of plunger 24 in its home, unactuated position. At all other times, knee 20a bears against the upper end of plunger 26. Conduit 60 secured to nipple 62 introduces pressurized air from a re mote source, not shown, into the interior of handball 16.

CYCLE OF OPERATION The cycle of operation of handball 10 will now be described with particular reference to FIGS. 1 and 6.

When trigger lever 20 is in its neutral, or home position, plunger 24 is urged upwardly by check valve spring 58 to a position in proximity to knee 20a on lever 20. The pressurized air supply entering handball through conduit 60 travels but a short distance before encountering ball check valve 156 which is biased into engagement by lower control spring 158 with a shoulder in passageway 146. Some of the air escapes past valve 156 and travels axially upwardly through passageway 146, flows between seat 144 and washer 140 and exits through exhaust port 66. Some of the air enters radial passage 70, and escapes past valve 56 in bore 16, then travels axially upwardly through passageway 46, flows between seat 44 and washer 40 (see FIG. 3) and exits through common exhaust port 66.

As the operator manipulates trigger lever 20 with his thumb, knee 20a on the lever presses against the upper surface of plunger 24 to overcome the bias of spring 30 and shift the plunger downwardly a short distance until washer 40 engages seat 44 in plug 42. The extent of movement required for the washer to contact the seat is 0.010 inches, although this distance is not a critical one.

Continued pivotal movement of lever 20 shifts plunger 24 and spacer 34, which move in concert, slightly further downwardly and such movement causes the engagement of washer 40 upon valve seat 44 in plug 42. Needle-like segment 37 on pin 37 unseats ball valve 56 from its blocking position in axial passageway 46 in plug 42. The pressurized air being supplied over conduit 60 then passes through nipple 62 into passageway 46, flows past unseated ball valve 56, and moves upwardly until meeting washer 40, which as noted previously, is now securely positioned upon seat 44.

Some of the pressurized air escapes past seat 44 and flows into radial passage 64 and then to exhaust port 66, but the bulk of the pressurized air is blocked by the washer and thus causes a buildup of backpressure in axial passage 46, radial passageway 54 and first signal port 55. As increased force is applied to plunger 24 by the continued pivotal movement of trigger lever 20, the contact pressure between washer 40 and seat 44 is increased. lncreased contact pressure reduces the air flow past seat 44 and increases the backpressure created at first signal port 55. Consequently, the variable air pressure signal produced at port 55 is proportional to the pivotal displacement of trigger lever 20. Trigger lever 120 functions in the same manner and generates a variable air pressure signal at second signal port 1155.

The pneumatic circuit of FIG. 7 schematically depicts the relationship of handball 10 to the remainder of the pneumatic control system that, in turn, controls the operation of the hydraulic control valve which governs the performance of machine functions for a mobile construction machine. Examining the circuit in detail, pressurized air from a supply source, such as a compressor, is fed to pressure regulator 200. In a representative circuit, the pressurized air is supplied to regulator 200 at 85l20 p.s.i. and the regulator reduces the pressure to 35 psi. The pressurized air then. passas through conduit 60 into handball 10. Flow through handball 10 is substantially blocked by spring loaded ball valve 56 in axial passageway 46 when trigger lever 20 is in its normal, unactuated position, as indicated by the dotted lines. When trigger lever 20 is pivoted away from its unactuated position and exerts pressure on plunger 24 (see MG. 6), ball valve 56 is unseated and a back pressure signal of variable magnitude is created at first signal port 55 by the modulating valve defined between washer 40 and seat 44. The magnitude of the back pressure signal (AX) is directly proportional to the extent of movement (X) of trigger lever 20. In a representative circuit, the variable back pressure air signal varied in magnitude over a range of 10 to 35 p.s.1.

The variable pressure air signal flows into amplifierregulator 202, which is pressurized from the power source at -120 p.s.i. The air signal adjusts the air signal exiting from amplifier-regulator 202 to a lever ranging from 30-105 p.s.i., the pressure regulation function being achieved in a 3:1 ratio. If desired, regulator 202 could be omitted from the circuit and the air signal from handball 10 could be used to directly operate another device.

In the preferred and illustrated circuit, however, the air signal then passes through quick release valve 204 and actuates air cylinder 206 which is connected to hydraulic control valve 208. Valve 204 may be omitted from the pneumatic circuit, if desired if the valve 202 does not provide additional response towards the center portion of valve 208.

Actuation of air cylinder 206 provides the impetus necessary for operation of hydraulic control valve 208. Operation of valve 208 governs, in turn, the operation of hydraulic cylinder 210 which controls the functions performed by construction machines. By virtue of the above described circuitry, the speed of movement of cylinder 210 is proportional to the magnitude of the air pressure signal present at first signal port 55.

Trigger lever controls an identical, but separate, pneumatic circuit (not shown) in an identical manner by means of the air pressure signal present at second control port 155. Trigger lever 120 proportionately controls a second air cylinder 212, which adjusts hydraulic control valve 208 and thus hydraulic cylinder 2110. Valve 208 may assume the form of a spool valve which could be readily retained in a central position by unactuated air cylinders 206 and 212, and could easily be shifted in either direction from such position in response to a low level air signal at air cylinders 206 or 212. The hydraulic fluid for cylinder 212 is retained in reservoir 2113.

While FIGS. 1-7 show handball 10 secured to the upper end of control lever 14, FIG. 8 shows the handball and lever in combination with a mobile construc tion machine. It should be noted that the handballs and/or levers can be adapted to function remotely by utilizing quick connect-disconnect joints and elongated conduits (not shown). The ready removability of either or both of these components can be of particular significance when digging a deep trench or when laying pipe in such trench with a backhoe. With conventional controls, the machine operator often is unable to see down into the trench and must estimate the position the backhoe bucket has assumed. The provision of readily detachable control units and related pneumatic control circuitry would permit machine operator mobility for peering into the trench for carefully and accurately controlling the functions of the mobile construction machine.

Manifestly, numerous modifications, omissions and refinements in the above described handballs and related pneumatic circuitry will become apparent to the skilled artisan from the foregoing description. Consequently, such description should be interpreted as being illustrative, and non-limiting in nature.

We claim:

1. in combination, a mobile construction machine, pressure responsive pneumatic circuitry including inlet means and outlet means for controlling the functions of said machine, and a handball for producing a variable pressure signal, said handball comprising:

a. a body including an axial bore extending therethrough,

b. said body also including an inlet port, an exhaust port, and a signal port communicating with said axial bore, said signal port being connected to the inlet means of said pneumatic circuitry,

c. normally unactuated trigger means mounted at one end of said axial bore,

d. a plug having an axial passageway therethrough secured within the end of the axial bore in the handball opposite to said trigger means,

e. an annular valve seat being defined at the inner end of said plug,

f plunger means mounted for axial movement within said bore between unactuated and fully actuated positions, said plunger means located in proximity to said trigger means,

g. supply means connected to said inlet port for delivering pressurized fluid thereto,

it. normally opened valve means situated within said axial bore for metering the flow of fluid passing between said inlet port and said exhaust port, said valve means including a first washer operatively connected to said plunger means for axial movement relative to said valve seat,

. said trigger means, when actuated, moving said plunger means and said first washer toward said valve seat to produce a modulated pressure signal at said signal port that is fed to the inlet means of said pneumatic circuitry, said signal being proportional to the extent of movement of said plunger means.

2. The combination as defined in claim 1 wherein said plunger means within said handball includes a cylindrical plunger and said valves means includes, spacer means disposed in operative relationship to said plunger, and means interconnecting the plunger and the spacer means so that they move in concert with one another.

3. The combination as defined in claim 2 wherein said plunger has a lower end of reduced dimension, and said means interconnecting the plunger and the spacer means comprises a second washer retained upon the lower end of said plunger and resting upon said spacer means, and a control spring rests upon said second washer and encircles the lower end of said plunger.

4. The combination as defined in claim 2 wherein said spacer means includes a pin adjustably secured thereto and extending away from said spacer means.

5. A handball as defined in claim 4 wherein said spacer means comprises a body member having a top wall, a bottom wall, an annular wall joining the top and bottom walls, a cavity formed in the top wall and extending downwardly toward the bottom wall, and an opening in the bottom wall extending upwardly toward said cavity, said pin being adjustably inserted into said opening in said body member.

6. A handball as defined in claim 1 wherein a recess is formed in the body member of the handball and said trigger means extend thereinto, pin means extend across said recess to mount said trigger means for pivotal movement, and a knee on said trigger means is disposed in proximity to, and in alignment with, the upper end of said plunger means.

7. in combination, a mobile construction machine, pressure responsive pneumatic circuitry including inlet means and outlet means for controlling the functions of said machine, and a handball for producing a variable pressure signal, said handball comprising:

a. a body including an axial bore extending therethrough,

b. said body also including an inlet port, an exhaust port, and a signal port communicating with said axial bore, said signal port being connected to the inlet means of said pneumatic circuitry,

c. normally unactuated trigger means mounted at one end of said axial bore,

. plug means secured within the end of the axial bore opposite to said trigger means, said plug means having an axial passage for establishing communication between said bore and said inlet port,

e. normally closed check valves located within said axial passageway for blocking such communication,

plunger means mounted for axial movement within said bore, said plunger means located in proximity to said trigger means,

said plunger means including a cylindrical plunger, spacer means disposed in operative relationship to said plunger, and means interconnecting the plunger and the spacer means so that they move in concert with one another,

h. said spacer means includes a pin adjustably secured thereto and extending away from said spacer means into contact with said check valve means,

. supply means connected to said inlet port for delivering pressurized fluid thereto,

j. normally opened valve means situated within said axial bore for metering the flow of fluid passing between said inlet port and said exhaust port.

It. said trigger means, when actuated, moving said plunger means to close said valve means and produce a pressure signal at said signal port that is fed to the inlet means of said pneumatic circuitry.

8. A pneumatic control for controlling functions of a mobile construction machine, said control comprising:

a. a body including an axial bore extending therethrough,

b. said body also including an inlet port, an exhaust port and a signal port communicating with said axial bore,

c. manually actuatable plunger means mounted for axial movement within said bore between unactuated and fully actuated positions, supply means connected to said inlet port for delivering fluid under pressure thereto,

2. valve means in said bore for substantially closing said inlet port from said exhaust and signal ports when said plunger means is in said unactuated position,

valve actuating means located in said bore,

resilient means connecting said plunger to said valve actuating means for permitting concurrent movement of said plunger and valve actuating means to open said valve means and permitting relative movement of said plunger with respect to said mobile construction machine, said control comprising:

a. a body including an axial bore extending therethrough,

b. said body also including an inlet port, an exhaust port and a signal port communicating with said axial bore,

c. manually actuatable plunger means mounted for axial movement within said bore between unactuated and fully actuated positions,

d. supply means connected to said inlet port for delivering fluid under pressure thereto,

e. valve means in said bore for substantially closing said inlet port from said exhaust and signal ports when said plunger means is in said unactuated positron,

f. valve actuating means located in said bore and being connected to said plunger means for concurrent movement of said plunger and said valve actuating means to open said valve means, upon actuation of said plunger means, and

g. pressure modulating means including a sealing element mounted on said valve actuating means for concurrent movement therewith into contact with an annular seat in said bore to increasingly restrict flow from said inlet to said exhaust ports as said plunger is moved from its unactuated position toward its fully actuated position,- thus increasing the pressure at said signal port proportionally with the extent of movement of said plunger. 

1. In combination, a mobile construction machine, pressure responsive pneumatic circuitry including inlet means and outlet means for controlling the functions of said machine, and a handball for producing a variable pressure signal, said handball comprising: a. a body including an axial bore extending therethrough, b. said body also including an inlet port, an exhaust port, and a signal port communicating with said axial bore, said signal port being connected to the inlet means of said pneumatic circuitry, c. normally unactuated trigger means mounted at one end of said axial bore, d. a plug having an axial passageway therethrough secured within the end of the axial bore in the handball opposite to said trigger means, e. an annular valve seat being defined at the inner end of said plug, f. plunger means mounted for axial movement within said bore between unactuated and fully actuated positions, said plunger means located in proximity to said trigger means, g. supply means connected to said inlet port for delivering pressurized fluid thereto, h. normally opened valve means situated within said axial bore for metering the flow of fluid passing between said inlet port and said exhaust port, said valve means including a first washer operatively connected to said plunger means for axial movement relative to said valve seat, i. said trigger means, when actuated, moving said plunger means and said first washer toward said valve seat to produce a modulated pressure signal at said signal port that is fed to the inlet means of said pneumatic circuitry, Said signal being proportional to the extent of movement of said plunger means.
 2. The combination as defined in claim 1 wherein said plunger means within said handball includes a cylindrical plunger and said valves means includes, spacer means disposed in operative relationship to said plunger, and means interconnecting the plunger and the spacer means so that they move in concert with one another.
 3. The combination as defined in claim 2 wherein said plunger has a lower end of reduced dimension, and said means interconnecting the plunger and the spacer means comprises a second washer retained upon the lower end of said plunger and resting upon said spacer means, and a control spring rests upon said second washer and encircles the lower end of said plunger.
 4. The combination as defined in claim 2 wherein said spacer means includes a pin adjustably secured thereto and extending away from said spacer means.
 5. A handball as defined in claim 4 wherein said spacer means comprises a body member having a top wall, a bottom wall, an annular wall joining the top and bottom walls, a cavity formed in the top wall and extending downwardly toward the bottom wall, and an opening in the bottom wall extending upwardly toward said cavity, said pin being adjustably inserted into said opening in said body member.
 6. A handball as defined in claim 1 wherein a recess is formed in the body member of the handball and said trigger means extend thereinto, pin means extend across said recess to mount said trigger means for pivotal movement, and a knee on said trigger means is disposed in proximity to, and in alignment with, the upper end of said plunger means.
 7. In combination, a mobile construction machine, pressure responsive pneumatic circuitry including inlet means and outlet means for controlling the functions of said machine, and a handball for producing a variable pressure signal, said handball comprising: a. a body including an axial bore extending therethrough, b. said body also including an inlet port, an exhaust port, and a signal port communicating with said axial bore, said signal port being connected to the inlet means of said pneumatic circuitry, c. normally unactuated trigger means mounted at one end of said axial bore, d. plug means secured within the end of the axial bore opposite to said trigger means, said plug means having an axial passage for establishing communication between said bore and said inlet port, e. normally closed check valves located within said axial passageway for blocking such communication, f. plunger means mounted for axial movement within said bore, said plunger means located in proximity to said trigger means, g. said plunger means including a cylindrical plunger, spacer means disposed in operative relationship to said plunger, and means interconnecting the plunger and the spacer means so that they move in concert with one another, h. said spacer means includes a pin adjustably secured thereto and extending away from said spacer means into contact with said check valve means, i. supply means connected to said inlet port for delivering pressurized fluid thereto, j. normally opened valve means situated within said axial bore for metering the flow of fluid passing between said inlet port and said exhaust port. k. said trigger means, when actuated, moving said plunger means to close said valve means and produce a pressure signal at said signal port that is fed to the inlet means of said pneumatic circuitry.
 8. A pneumatic control for controlling functions of a mobile construction machine, said control comprising: a. a body including an axial bore extending therethrough, b. said body also including an inlet port, an exhaust port and a signal port communicating with said axial bore, c. manually actuatable plunger means mounted for axial movement within said bore between unactuated aNd fully actuated positions, d. supply means connected to said inlet port for delivering fluid under pressure thereto, e. valve means in said bore for substantially closing said inlet port from said exhaust and signal ports when said plunger means is in said unactuated position, f. valve actuating means located in said bore, g. resilient means connecting said plunger to said valve actuating means for permitting concurrent movement of said plunger and valve actuating means to open said valve means and permitting relative movement of said plunger with respect to said valve actuating means when said valve means has been opened, h. pressure modulating means including a sealing element mounted on said valve actuating means for concurrent movement therewith into contact with an annular seat in said bore to increasingly restrict flow from said inlet to said exhaust ports as said plunger is moved from its unactuated toward its fully actuated position, thus increasing the pressure at said signal port proportionally with the extent of movement of said plunger.
 9. A pneumatic control for controlling functions of a mobile construction machine, said control comprising: a. a body including an axial bore extending therethrough, b. said body also including an inlet port, an exhaust port and a signal port communicating with said axial bore, c. manually actuatable plunger means mounted for axial movement within said bore between unactuated and fully actuated positions, d. supply means connected to said inlet port for delivering fluid under pressure thereto, e. valve means in said bore for substantially closing said inlet port from said exhaust and signal ports when said plunger means is in said unactuated position, f. valve actuating means located in said bore and being connected to said plunger means for concurrent movement of said plunger and said valve actuating means to open said valve means, upon actuation of said plunger means, and g. pressure modulating means including a sealing element mounted on said valve actuating means for concurrent movement therewith into contact with an annular seat in said bore to increasingly restrict flow from said inlet to said exhaust ports as said plunger is moved from its unactuated position toward its fully actuated position, thus increasing the pressure at said signal port proportionally with the extent of movement of said plunger. 